Boring is the enlarging and truing of a hole by removing material from internal surfaces with a single-point cutter bit. On the lathe, boring is accomplished in either of these two methods: 1) mounting the holder and boring tool bar with cutter bit on the tool post and revolving the workpiece; or 2) mounting the workpiece in a fixed position to the carriage and revolving the boring tool bar and cutter bit in a chuck attached to the headstock spindle. (This is a special process and not used in most machine shops).
The workpiece may be supported in a chuck or fastened to a faceplate for boring operations depending upon the type of machine tool. When boring is to be performed on the ends of long stock needing additional support, the workpiece is mounted in a chuck and a steady rest is used to support farthest from the chuck. Some boring operations require the use of special chuck-mounted mandrels to hold workpieces that cannot be successfully mounted otherwise.
Boring is necessary in many cases to produce accurate holes. Drilled holes are seldom straight due to imperfections in the material which cause drills to move out of alignment. Therefore, where accuracy is important, drilled holes are usually made undersize and then bored or reamed to the proper dimensions.
A proper setup for boring requires that the correct boring tool is selected (not too long and not too small) and that the cutting insert mounted in the boring tool is set on center in the x-axis with the workpiece material.
Traditionally, boring bars are manufactured with one or multiple flats along the length of shank that are used to align the boring bar to the x-axis or on center to the workpiece. However, the addition of alignment flats reduces dynamic and static stiffness of the cutting tool. When the flats are used on long overhang tunable tooling, the reduction in stiffness greatly impacts the performance of the tool. If the flats are removed from the shank, such is often the case with tunable boring bars, the end user has no means to easily align the boring bar on center. The only possible way the end user can align the cutting tool on center is by scribing a line across the face of the workpiece with a cutting tool on the turret that is known to be calibrated on center, and then rotate the boring bar in the holder until the cutting edge is on center. However, this method can be cumbersome and the end user may not always have the option of scribing a permanent line on the face of the workpiece.
Therefore, it is desirable to provide a method and apparatus that provides center height alignment of the boring bar without the need to scribe a permanent line on the face of the workpiece or without the use of flats on the shank of the boring bar.